The aim of this study was to investigate the antibacterial effect of a diode laser in deep root canal dentin. The microbial colonization of root canal dentin can lead to failures in conventional endodontic treatment if an inadequate bacterial reduction only is achieved through canal treatment and chemical disinfection. 100 microm, 300 microm and 500 microm bovine dentin slices obtained by longitudinal sections were sterilized and inoculated on one side with an Enterococcus faecalis suspension. Laser radiation was performed on the opposite side with the diode laser (810 nm) at a setting of 3 W in continuous mode (CW). Radiation was performed using a 400-microm tapered fiber tip at an angle of approximately 5 degrees to the surface over a period of 30 seconds. The output power at the distal end of the tip was 0.6 W. The bacteria were then eluted through vibration and cultured on blood agar plates. The colony count reflected the antibacterial effect of laser radiation as a function of the layer thickness. A mean bacterial reduction of 74% was achieved even with a 500-microm thick slice. This investigation indicates that the diode laser radiation reduces the number of bacteria in deep layers of infected root canal wall dentin.

Members of the domain Archaea , one of the three domains of life, are a highly diverse group of prokaryotes, distinct from bacteria and eukaryotes. Despite their abundance and ubiquity on earth, including their close association with humans, animals, and plants, so far no pathogenic archaea have been described. As some archaea live in close proximity to anaerobic bacteria, for instance, in the human gut system and in periodontal pockets, the aim of our study was to assess whether archaea might possibly be involved in human endodontic infections, which are commonly polymicrobial. We analyzed 20 necrotic uniradicular teeth with radiographic evidence of apical periodontitis and with no previous endodontic treatment. Using real-time quantitative PCR based on the functional gene mcrA (encoding the methyl coenzyme M reductase, specific to methanogenic archaea) and on archaeal 16S rRNA genes, we found five cases to be positive. Direct sequencing of PCR products from both genes showed that the archaeal community was dominated by a Methanobrevibacter oralis -like phylotype. The size of the archaeal population at the diseased sites ranged from 1.3 × 10 ⁵ to 6.8 × 10 ⁵ 16S rRNA gene target molecule numbers and accounted for up to 2.5% of the total prokaryotic community (i.e., bacteria plus archaea). Our findings show that archaea can be intimately connected with infectious diseases and thus support the hypothesis that members of the domain Archaea may have a role as human pathogens.

Human subgingival plaque biofilms are highly complex microbial ecosystems that may depend on H ₂ -metabolizing processes. Here we investigated the ubiquity and proportions of methanogenic archaea, sulfate reducers, and acetogens in plaque samples from 102 periodontitis patients. In contrast to the case for 65 healthy control subjects, hydrogenotrophic groups were almost consistently detected in periodontal pockets, with the proportions of methanogens and sulfate reducers being significantly elevated in severe cases. In addition, antagonistic interactions among the three microbial groups indicated that they may function as alternative syntrophic partners of secondary fermenting periodontal pathogens.